Engineering Chemistry S Datta

VALENCY AND CHEMICAL BONDING 37
Q. 9. What are polar and non-polar covalent bonds?
Ans. A nonpolar bond is formed when sharing takes place between the atoms of same
electronegativity i.e., between similar atoms during bond formation. e.g.,
H—H, O = O, Cl—Cl, Br—Br, etc.
A polar bond is formed when sharing takes place between the atoms of different
electronegativities i.e., between dissimilar atoms during bond formation viz.,
H +δ ⎯→ Cl –δ
Q. 10. What is the special feature of a covalent bond?
Ans. (a) Covalent bond holds together the atoms of nonmetals in a molecule and giant
structures. (b) Molecules have a definite shape because covalent bonds have a definite length
and direction.
Q. 11. What is covalent radius?
Ans. The covalent radius of an element is half the bond length. When two atoms of the
element (same or different) are joined by a single covalent bond, the length of single covalent
bonds between atoms of different elements can be determined fairly accurately by adding the
covalent radii of the two atoms. Covalent radius of an atom is half of the distance between the
nuclei of two like atoms bonded together by a single covalent bond.
Covalent radius
0.037 nm H2
Covalent radius
0.104 nm Cl2
Bond length
0.141 nm sum of
covalent radii HCl
Fig. 2.37 (b) Forces of attraction during H 2
molecule formation.
Covalent radius = 0.114 nm
van der Waals radius 0.190 nm. van der Waals
radii determine the effective size of a molecule.
van der Waals radius is the effective radius of an
atom when held in contact with another atom by
weak intermolecular forces.
Fig. 2.37 (c) Covalent and van der Waals radii for bromine.
Q. 12. Mention special types of bonds.
Ans. (i) Metallic bond, (ii) van der Waals bond, (iii) Hydrogen bond.
Q. 13. What is the special feature of a coordinate bond?
Ans. This type of bond is formed by unequal sharing of electron pair, one of the
participating atoms in the bond formation donates both the electrons for bond formation. The
coordinate bond is indicated by an arrow to express this unequal sharing.